Ranganathan's Canons of Characteristics: A Practical Analysis

This article explains the canons of characteristics in the idea plane with practical examples.

In S.R. Ranganathan’s theory of library classification, the canons of characteristics in the idea plane are the fundamental principles that dictate which characteristics of subjects should be used to define classes, and how those characteristics should function to ensure a classification system is logical, stable, and useful [1][2][3].

What is the Idea Plane?

The idea plane is the conceptual level where we analyze subjects and their relationships before choosing terms (verbal plane) or symbols (notation plane) to represent them. In this phase, we:

• Analyze the universe of knowledge.
• Identify characteristics that can divide subjects into classes.
• Determine how those classes should be arranged [1][4][5].

The canons of characteristics represent the primary set of rules within this idea plane.

The Four Canons of Characteristics

Ranganathan specifies four essential canons for characteristics [2][3]:

1. Canon of Difference
2. Canon of Ascertainability
3. Canon of Relevance
4. Canon of Permanence

Each is detailed below with illustrative examples.

1. Canon of Difference

Statement: The characteristics used to divide a class must differentiate the resulting subclasses; they must not be common to all members of the class.

Meaning: If a characteristic is shared by every item in a class, it cannot be used to subdivide that class further.

Example: Consider the class Books:

• “Being made of paper” cannot be used to divide books into subclasses, because all books share this trait.
• “Subject” (e.g., History, Science, Literature) can be used, because books differ by subject [6][3].

Example: Class Plants:

• “Being living” differentiates plants from non-living things but not within the plant category itself.
• “Mode of reproduction” (sexual vs. asexual) or “Type of stem” (herbaceous vs. woody) does differentiate plants, making them valid characteristics [6].

2. Canon of Ascertainability

Statement: The chosen characteristic must be ascertainable—it must be identifiable clearly and consistently for each item.

Meaning: If a characteristic is vague, subjective, or impossible to measure reliably, it should not be used.

Example: Class Novels:

• “Popularity” is not a good characteristic, as it is subjective and changes over time.
• “Time of setting” (ancient, modern) or “Genre” (mystery, romance) is ascertainable and consistent [6][3].

Example: Class Artists:

• “Fame” is not ascertainable in a stable way.
• “Period” (Renaissance, Modern) or “Nationality” is ascertainable and suitable for classification [6].

3. Canon of Relevance

Statement: The characteristic must be relevant to the purpose of the classification and the needs of the library users.

Meaning: Even if a characteristic is distinct and ascertainable, it must be meaningful to how users seek and utilize materials.

Example: Class Medicine:

• “Place of publication” may be distinct, but for medical library users, it is not relevant to finding information on treatments.
• “Body system” (cardiology, dermatology) or “Type of intervention” (surgery, pharmacology) is highly relevant [6][3].

Example: Class Newspapers:

• “Color of paper” is irrelevant.
• “Subject coverage” (local, national, business) is highly relevant for archiving and retrieval [5].

4. Canon of Permanence

Statement: The characteristic should be permanent or stable over time, rather than prone to frequent change.

Meaning: Changing characteristics lead to frequent, costly, and confusing reclassification.

Example: Class Persons (e.g., authors):

• “Current address” is not permanent; people move.
• “Nationality” or “Academic discipline” is more permanent and suitable for classification [6][3].

Example: Class Newspapers:

• “Current editor” changes often and is not ideal.
• “Place of publication” or “Language” is more permanent and suitable for organizing archives [5].

How the Four Canons Work Together

For a characteristic to be acceptable in the idea plane, it should ideally satisfy all four canons:

• Differentiate: (Canon of Difference)
• Clearly Identifiable: (Canon of Ascertainability)
• Useful to Users: (Canon of Relevance)
• Stable Over Time: (Canon of Permanence)

Composite Example: Newspaper Archive

When classifying a newspaper collection:

1. Language: Satisfies all four canons (Different, Ascertainable, Relevant, Permanent) → Good characteristic.
2. Current Price: Fails Relevance and Permanence (changes often) → Not suitable.
3. Place of Publication: Satisfies all four canons → Good characteristic.

Summary

The canons of characteristics in the idea plane are:

• Canon of Difference: Characteristics must create real distinctions.
• Canon of Ascertainability: Characteristics must be identifiable and consistent.
• Canon of Relevance: Characteristics must matter to users and the collection's purpose.
• Canon of Permanence: Characteristics should be stable over time.

These canons ensure that when you analyze subjects—whether biological sciences, newspaper topics, or library materials—your classification remains logical, practical, and durable [1][2][3].